1. Field
The present invention relates to a capo for a stringed musical instrument, in particular to improvements to lever arm type capos.
2. Background Art
A capo, sometimes variously termed a capodastro, capodaster, capo tasto or cejilla, is a well-known device used with a stringed instrument, for example a guitar or banjo, which has a neck and a set of strings extending along the length of the neck. The capo, when applied, serves to clamp the strings against the fingerboard provided along the neck, and in particular against one of the number of fret bars disposed along the length of the fingerboard, to reduce the effective length of the strings and therefore adjust the pitch produced by the strings.
A large number of different capos, divided into different basic types exist. Each different type of capo has very different advantages and technical considerations. Players often have preferences for different types of capo. Manufacturers conventionally develop the different types of capos separately and independently in particular due to the different characteristics of the different types of capos and due to customer preferences for the different types.
One type of capo is a lever arm type positive locking capo. A commercially successful example of this type of capo is described in U.S. Pat. No. 4,250,790. This capo comprises a top arm that bears against the strings and which is connected to a side arm extending laterally of the instrument neck. Pivotally attached to the side arm are a lower arm which extends under the back of the instrument neck, and a lever arm located below the lower arm. An adjusting screw extends through the lever arm to bear against the lower surface of the lower arm when the lever member is pivoted toward the jaw member. As the lever member is pivoted toward the lower arm, the tip of the adjusting screw abuts against a rear abutment surface of the lower arm urging the lower arm towards the top arm whereby the upper surface of the lower arm engages the back of the instrument neck and the top arm depresses the strings against the fingerboard on the top of the neck. The arrangement is such that further pivoting of the lever arm is arranged to then cause the tip of the adjustment screw to move along the rear abutment surface to and beyond an over-centre point and maximum deflection of the lower arm by the tip of the adjustment arm. At that point the lever arm is then biased and urged against the lower arm and the lower arm is then locked in a closed position. The adjusting screw may be advanced or backed off to vary the extent to which the jaw member closes before over centre point and locking of the capo is reached, thereby allowing the capo to accommodate varying sizes of instrument neck, and allowing the user to regulate the pressure exerted by the capo on the instrument strings.
Despite the commercial success of the capo described in U.S. Pat. No. 4,250,790 over a number of years there are problems which have not to date, despite the time over which this capo has been available, been recognised or addressed and which have generally been overlooked. In particular this type of capo is in fact relatively difficult to apply and generally needs two hands to fit to an instrument. In addition the arms when the capo is not in use and attached to the instrument are prone to dangle and freely pivot and flap about preventing easy application to the guitar neck. Furthermore the adjuster screw and linkages are subject to various lateral and shear loads. This induces stresses within the assembly and also in relation to lateral loads on the adjuster screw increase the friction on the threads making adjustment more difficult. The operation can also be improved, in particular to provide improved locking and prevent ‘drop off’ resistance. In particular the disposition of the adjusting screw relative to the lower arm leads to differential “drop off” across the operating range of the capo. Indeed an improvement to this capo to address this problem is described in U.S. Pat. No. 5,792,969 and WO9849669, and another similar arrangement is described in US 2005/0087056. The overall appearance of the capo can also be improved.
Other examples of lever arm capos are also described in U.S. Pat. No. 360,612; U.S. Pat. No. 468,193; U.S. Pat. No. 4,149,443; U.S. Pat. No. 4,104,947, and US 2008/0168882. U.S. Pat. No. 360,612, U.S. Pat. No. 468,193, and U.S. Pat. No. 4,149,443 which again date back over a number of years do not include suitable adjustment arrangements to accommodate different sizes of neck while achieving positive locking. In relation to U.S. Pat. No. 468,193 and US 2008/0168882 locking is in particular achieved by a spring load such that it is not positively locked and the locking and load is less than ideal such that the strings may not be sufficiently clamped to give a crisp note, and/or the capo may become dislodged.
Such lever type capos, in particular an adjustable lever arm type capo can therefore be further improved.